Effects of Chronic Exposure to Ultraviolet B Radiation on DNA Repair in the Dermis and Epidermis of the Hairless Mouse

It has previously been shown that chronic exposure to low fluences of ultraviolet B radiation reduced DNA repair capacity in mouse skin. In this study we now extend this to examine the concentration dependence and tissue dependence of this phenomenon. We found that (6–4) photoproducts were repaired considerably faster than cyclobutane dimers and that the kinetics for photoproduct removal were comparable in the dermis and epidermis. Chronic ultraviolet B irradiation significantly reduced the initial rate and extent of DNA repair. After low daily doses of ultraviolet B (6–4) photoproduct repair was most affected and after high daily doses the repair of both cyclobutane and (6–4) dimers was reduced. Whereas cyclobutane dimer repair was most affected in the dermis, reduced (6–4) photoproduct repair was observed in both tissues. The deleterious effects of chronic ultraviolet exposure were sustained for a considerable time after the chronic treatment ended